1. Field of the Invention
The present invention relates to an object picking system for picking up, one by one, a plurality of objects. The present invention may be used, for example, in an operation of picking workpieces, irregularly accommodated in a container or the like in a factory, one by one from the container.
2. Description of the Related Art
In a case where, in a production line in a factory for example, a multiplicity of workpieces are placed in a container in an irregular and random arrangement, it is advantageous in view of labor saving that the workpieces are individually picked up safely and reliably while their configuration is not substantially changed. It is conventionally known to carry out such an operation of picking up workpieces by using a robot system provided with a visual sensor for detecting the position, orientation, etc., of the workpieces. In a case where the robot system is used to carry out the picking-up operation on workpieces arranged irregularly in a container, it is possible, if there is no other workpiece superimposed on or overlapping with a workpiece required to be picked up (hereinafter referred to as a “workpiece to be picked”), to control a robot mechanical section on the basis of the appearance information of the workpiece obtained by a visual sensor, etc., so as to hold and pick up the workpiece to be picked by a usual picking-up operation.
However, if another workpiece is at least partially superimposed on the workpiece to be picked, and when the workpiece to be picked is picked up while maintaining such a condition, the other workpiece superimposed on the workpiece to be picked may fall down and drop into the container or may be thrown out in the factory during a subsequent transferring operation. The dropping workpiece may collide with another workpiece, which may cause the damage of the workpieces or noise due to collision.
In the above situation, a conventional robot system generally performs a workpiece picking operation in such a way that the highest priority is placed on the safety of operators. Thus, when the visual sensor detects that another workpiece is at least partially superimposed on the workpiece to be picked, the system defers the picking-up operation on this workpiece to be picked, and tries to pick out another secondary workpiece to be picked, with which no workpiece overlaps. For example, Japanese Unexamined Patent Publication (Kokai) No. 9-91441 (JP-A-9-91441) discloses an interference detecting method, performed in an article picking system using a robot, in which an “interference” (i.e., contact, proximity, overlap) between an objective article to be picked and another article is detected by means of image processing.
However, in the above technique in which the picking operation for the workpiece to be picked but interfering with another workpiece is deferred, it may finally be impossible to pick up the deferred workpiece, depending on the superposition of the workpieces. In this case, all the workpieces lying under the deferred workpiece to be picked can never be picked up, and this may lead to the significant lowering of working efficiency.